There is a particularly popular type of small watercraft which is known as a "personal watercraft." This type of watercraft is a type in which one or more passengers ride on, rather than in, the watercraft. The personal watercraft is characterized by having a pair of handlebars, and straddle-type seat disposed generally above the engine. These watercraft are primarily recreational in nature. Generally, this type of watercraft is powered by a jet propulsion drive unit (sometimes called a jet-pump) which is positioned in a tunnel formed on the underside of the hull. This type of watercraft is quite compact in its nature.
In connection with these types of watercraft, problems have been encountered in connection with the treatment of the exhaust gases. Particularly, it is important to provide an efficient discharge for the exhaust gases that will not create excess back pressure which can deteriorate engine performance, but effective silencing also must be accomplished.
Several types of exhaust treatment have been proposed for discharge and silencing of exhaust gases from jet propelled watercraft. In one of these types of systems the exhaust gases flow through one or more expansion chambers that are contained within the hull of the watercraft, the gases then being discharged through the side of the hull. This type of arrangement, however, does not always provide effective silencing.
Another type of exhaust system for jet propulsion powered watercraft discharges the exhaust gases either into the tunnel in which the jet propulsion unit is contained, or into the water being discharged from the discharge nozzle of the jet propulsion unit. This arrangement has also failed to be fully effective in exhaust silencing.
Yet another type of exhaust system is silenced by discharging the exhaust gases through an underwater exhaust gas outlet. However, this method of silencing has certain disadvantages caused primarily by the different speeds at which the watercraft may operate. For example, if the exhaust gases are discharged into the water at a level that is only slightly submerged when the watercraft is operating at low speeds, then the discharge may be too high and above the water when the watercraft is operating at high speeds. Alternatively, a lower discharge level, keeping it submerged at high speeds, may give rise to excessive back pressure of the exhaust gases when the watercraft is operating at low speeds.
Given the limitations of prior exhaust treatment designs it would be desirable to design an exhaust treatment system which used the efficient cooling of the surrounding water without reducing engine efficiency by high back pressures. The design and positioning of the exhaust outlets as found in the present invention provide such a solution.